1. Technical Field
The present invention is directed to controlling actuation of a vehicle passenger restraint system and is particularly directed to evaluating whether a vehicle crash condition is sufficient to warrant actuation of the restraint system.
2. Prior Art
Actuatable passenger restraint systems for vehicles are well known in the art. Such systems are used to sense a crash condition and, in response to such a condition, to actuate an airbag or lock a seat belt or actuate a pretensioner for a seat belt retractor.
The U.S. Pat. No. 3,870,894 to U. Brede et al. discloses an actuatable passenger restraint system employing an electrical transducer for providing an electrical signal indicative of a deployment condition, such as vehicle deceleration, for use in actuating such a restraint system. The transducer employed is a piezoelectric transducer operating as an accelerometer and provides an output signal having a value indicative of vehicle deceleration. That signal is then integrated and, when the integrated signal reaches a predetermined value, a trigger signal is provided for actuating the restraint system. However, if the output signal of the accelerometer decreases, the integrator is reset and the circuitry is conditioned for sensing another crash condition.
The U.S. Pat. No. 3,911,391 to M. Held is similar to that of Brede et al., but specifically provides that the integration of the output signal of the accelerometer will only commence when the output signal exceeds some minimum threshold level, thereby preventing triggering of the restraint system for deceleration values that can be safely absorbed by passengers in a vehicle.
The above noted patents to Brede et al. and Held have no provision for providing a trigger signal to actuate a restraint system when the output signal of the accelerometer momentarily falls below a minimum threshold value even though the output signal may have been greater than this level for a time duration indicative of a potentially valid crash condition.